1. Field of the Invention
The present Invention relates to a light attenuator which can approximately obtain constant outputting light strength and its attenuating method.
2. Description of the Related Art
In the adjustment of light strength of optical communication network or optical equipment, light attenuator is applied. Specially, with the development of recent transmitting system of Dense Wavelength Division Multiplexing (DWDM), the request with respect to the light attenuator is rapidly increasing. In the concrete, the light attenuator is used in the field of a light strength adjusting unit or a light amplifier of the translator in optical communication network. Also, the light attenuator is used in a light strength adjusting unit of optical equipment relating to a variety of light sources, for example, a laser diode (LD) light source or the like. Further, the light attenuator is used in a unit being for protecting a light detector to detect a high strength light.
In the light attenuators used for adjusting light strength or the like, currently, a fixed type and a variable type optical attenuating units are known.
On the one hand, the fixed type optical attenuating unit is used for obtaining predetermined attenuating amount by using attenuating filter or optical fiber added a attenuating dopant. In response to the attenuating amount, these fixed type optical attenuating units are classified.
On the other hand, the variable type optical attenuating unit includes a mechanical form light attenuator and a non-mechanical form light attenuator.
In the variable type optical attenuating units of mechanical, there are a type using a method which transfer light in space and attenuates the light; a type using a method which inserts a moveable attenuating optical filter into a light path; a type which quivers slightly optical fibers whose optical axes are corresponding to each other so as to cause a deviation between optical axes; and so on.
Also, in the variable type optical attenuating unit of non-mechanical, there are a Faraday effect type; a wave guide path type; a polymer wave guide path type using thermal optics; a Mach-Zehnder Mach-Zender. wave guide path (waveguide) type; and so on.
However, in the above prior art, there is a following subject to be solved.
For example, In the case that a optical communication network work is performed in which light strength in transferring path is changed, It is necessary to use a light attenuator whose attenuating amount must conform to the desired that in the transferring path.
Thus, when using a fixed type optical attenuating unit, because the attenuating amount of the fixed type optical attenuating unit is definite, to obtaining desired attenuating amount in the transferring path, the light attenuator is often exchanged with the attenuating amount in the transferring path changes. Because of this, there is a problem that, with the light strength changes sharply, It is impossible to correspond quickly to the change.
As compared with this, though the variable type optical attenuating unit has not the above problem like the fixed type optical attenuating unit, because the current variable type optical attenuating unit must be controlled electrically, electrical power is consumed. Moreover, when generating heat in using, because a driver is necessary for a attenuating amount control, the driver is assembled into a control unit. Therefore, there is a problem that the unit is large-sized.